Update sample so copying it displays a map

To avoid these issues, import any Leaflet methods asynchronously in response to the LMap component's `@ready` event:

```vue

<template>

  <l-map>

  <l-map style="height:50vh">

    <l-geo-json :geojson="geojson" :options="geojsonOptions" />

  </l-map>

</template>

<script>

// DON'T load Leaflet components here!

import { LMap, LGeoJson } from "./../../components";

// Its CSS is needed though, if not imported elsewhere in your application.

import "leaflet/dist/leaflet.css"

import { LMap, LGeoJson } from "@vue-leaflet/vue-leaflet";

export default {

  components: {